The effect of Euphorbia hirta leaf extract on the corrosion of aluminium in 0.5M HCl was investigated by using the gravimetric technique. It was shown that the presence of E. hirta leaf extract inhibited corrosion of aluminium in the test solutions and that the inhibition efficiency depended on the concentration of the plant extract as well as on the time of exposure of the aluminium samples in 0.5M HCl solutions containing the extract. The experimental data complied to Langmuir adsorption isotherm and the value and sign of the Gibb's free energy of adsorption obtained suggested that inhibitor molecules have been spontaneously adsorbed onto the aluminium surface through a physical adsorption mechanism
